1. Field of the Invention
The present invention relates to an image processing system, an image processing method, and a medium having an image processing control program recorded thereon. Particularly, the invention is concerned with an image processing system and method for executing an optimum image processing with use of a computer, as well as a medium having an image processing control program recorded thereon.
2. Description of the Prior Art
Heretofore, for image data of natural pictures such as photographs and image data of drawing type unnatural pictures, there have been known software such as photoretouch software for performing various effect processing. In such softwares, image data are displayed on a display or the like, to which an operator applies a desired processing to form nice-looking image data.
For example, in the case of reading a photograph through a scanner to obtain electronic image data, it is sometimes desired to highlight the contrast and vividness of the image.
As a method for enlarging the contrast of image data there is known the method disclosed in Japanese Patent Publication No.66318/95, in which the relation the luminance y before transformation and the luminance y′ after transformation are correlated with each other according to the following expression (1), and the luminance of image data is transformed on the basis of parameter ‘a’ or ‘b’ selected by an operator, whereby there is obtained a contrast-highlighted image from image data weak in contrast:y′=ay+b  (1)
On the other hand, as a method for highlighting saturation to highlight the vividness there is known a method wherein the value of a desired color component is increased in the case where the color components of image data are represented in terms of gradation data of red (R), green (G) and blue (B).
More particularly, when the gradation data is in the range of 0 to 255, 20 is always added to the gradation data of red to make red color more vivid, or 20 is always added to the gradation data of blue to make blue color more vivid.
Thus, among various effect processing there is included one which transforms natural pictures into more beautiful pictures, while some images are not required to be retouched, such as drawing type images.
In the latter case, in an image processing system using the above conventional software, the operator is required to judge the type of image on the display and select an appropriate effect processing from among various ones or judge the degree of the processing. Thus, it has been impossible to automate this operation.
For example, it has so far been impossible to judge automatically whether contrast should be highlighted or not or whether vividness should be highlighted or not.
In highlighting contrast, the conventional methods merely adopt the technique of providing plural settings different in strength of contrast beforehand and then switching over from one to another. Thus, it has been impossible to automatically select the most preferred one corresponding to the actual image data. Particularly, when luminance is changed in accordance with the foregoing expression (1), the result is such that only brightness is highlighted in the case of an image which is bright as a whole, or only darkness is highlighted in the case of an image which is dark as a whole.
Needless to say, the strength of contrast can be adjusted in television for example, but the parameter ‘b’, namely offset, is uniform and it has been impossible to effect an optimum highlighting for each individual image.
Also as to highlighting vividness, a man is required to judge to what degree of highlighting is to be performed with respect to each image data, and it has been impossible to select the best suited highlighting automatically.
Further, as to not only the contrast enlarging processing but also the saturation highlighting processing, there is a tendency to increase in value of image data. Therefore, if saturation is to be highlighted after highlighting of contrast, a loud image results. This is not desirable.
In this connection, in the above conventional image processing system, if one is adjusted to an appropriate condition and thereafter the other is adjusted, the result of the previous adjustment goes wrong and thus it is difficult to make adjustment as desired.
In U.S. Pat. No. 5,181,105 there is disclosed a technique of diminishing the contrast width of image data automatically in view of the point that a color space reproducible in a CRT display is larger than that in a video printer. In this case, all that is required is merely causing image data to enter the color space in the video printer which is known in advance. Thus, automation is feasible because only such reduction of the contrast width is needed irrespective of the type of image. Such an automation has nothing to do with the foregoing effect processing that intends to make the most of the image quality of the image data. Thus, the application of the aforesaid technique is meaningless.